doc: Add head ordering doc part

[mcmah309]

Document: #3756

I chose not to leak the implementation information here and rather advise users to not depend on ordering. Otherwise users depending on ordering may have negative downstream effects - changes to the implementation may case downstream code to break without users knowing why (which may happen between non-breaking semver versions), this can easily become out of date, ordering is already not guaranteed with async and changing components.

[jkelleyrtp]

This is fine for now, but we should really make the ordering stable. I'm not exactly sure how other frameworks go about this (namely effect ordering) but the fact that components don't run effects in a sensible order will lead to more bugs and quirks. I'd rather not have to document work-arounds and instead make this work predictably.

Documenting is fine as a stop-gap measure but we should try to fix the underlying issue. I've put this into our own bug backlog, but let's make sure the github issue stays around and tracks the bug properly.

[mcmah309]

Do you want me to close #3756 or is this the issue that was added to the backlog? If so, it should probably be renamed from "Document Level Tags Are Applied In Reverse Order" to "Stabilize Document Level Tag Ordering" and link back to this comment for future reference.